Fontawesome icons doesn't load in backend

[vtheod]

As I have recently discovered, there are some icons used by astroid that are not loaded by atum's fa css. For example fa-gear, fa-trash, fa-copy, fa-codepen, fa-heading etc.
This is happening only on j4.x which uses fa v5.15.4 and not on j5 which uses the latest fa.
As expected, you can face this issue only in article editing in the widgets section, not in astroid's panel.
This is more an atum's problem than astroid's, but it conflicts with our beloved framework...

I have checked this with more than two different installations, and it happens in every case.